1. Field of the Invention
This invention relates to a method and device for monitoring the soundness and quality of a twisted yarn produced in a double twist spindle of a twisting frame.
The invention is applicable to a double twist spindle for twisting together a number of yarns to form a twisted ply yarn. Said yarns can be of any composition or structure and will be known throughout the description and claims simply as yarns, whether they be in the form of filaments or filament complexes or natural or artificial fibres.
2. Description of the Related Art
The term "twist together" is used herein in the wide sense of combining two or more yarns, the wide sense including the twisting of ends of previously twisted single yarns. The invention is particularly useful for monitoring the twisting of two yarns, but can however be used for monitoring the twisted combination of three or more yarns, the limit being fixed only by practical considerations. It is well known that in a double twist spindle, the yarns to be twisted together are unwound upwards from at least two packages rotating about a fixed mandrel.
This well known unwinding operation has the drawback of causing the yarns to mutually interfere, they becoming interlaced before entering the central hole in the spindle to form loops, rings, corkscrew-like spiral parts and other shapes generally of this nature. It is also well known that yarns unwinding in a double twisting frame, especially at high speed, are exposed to a variation in tension, this latter sometimes becoming excessive. In the case of more than one yarn, whether yarns spun from staple or yarns formed from synthetic filaments, this excessive tension is undesirable because the yarns undergo severe stressing and rubbing contact on account of their mutual interference during their continuous unwinding from the feed packages, and consequently become excessively stretched, damaged or in the limit broken. In this respect, a single yarn often breaks, resulting in a yarn being collected which is no longer twisted with other yarns, hence leading to the formation of a defective bobbin. Such a defective bobbin compromises the subsequent working stages in the production process, and hence reduces the economy and productivity of plants of this kind. Again, the effect of mutual intersection and interweaving of the yarns and the effect of the said frequent sliding contact result in the formation of flying fibrils and sometimes loose yarn pieces which are often twisted together with the yarn, causing twisting defects. Double twist spindles of this type have the further drawback of being subjected to serious stressing due to the high rotational speed necessary to achieve maximum operating limits in terms of collection rate.
In operating current spindles, the often present wear and mechanical defects cause vibration and loss of spindle rpm, which directly affect the quality of the twisted yarn. In this respect, if this latter is formed in a twisting spindle which loses rotational speed for any mechanical reason, it becomes formed with an insufficient number of twists to provide correct strength, with resultant fairly frequent non-uniform twisting. This effect is undesirable because it ruins the appearance of the twisted yarn in that the individual yarn plies are loaded non-uniformly by the twisting. In the case of thin yarn subjected to particularly rapid unwinding, all this can produce breakage during the next stage of the production process.